1. Technical Field
The present disclosure relates generally to biocompatible implants and, more particularly, to intervertebral implants suitable for implantation into the lumbar, thoracic and/or cervical regions of the spine during a spinal fusion procedure.
2. Background of Related Art
Intervertebral implants for fusing together adjacent vertebrae of a spinal column are well known in the art. Such implants are formed in a variety of different shapes and sizes and are configured for insertion into receiving beds formed in the lumbar, thoracic and cervical regions of the spine. The implants may be formed from a variety of different biologically compatible materials including ceramics, polymers, human or animal bone, composites, etc. The implants may also be shaped to maintain the natural lordoses of the spine or to prevent the implant from backing out of an intervertebral receiving bed in which it will be implanted.
Examples of known implants are disclosed in U.S. Pat. No. 4,877,020 to Vich and U.S. Pat. No. 4,878,915 to Brantigan. Vich and Brantigan each disclose cylindrical implants having an outer helical thread formed thereabout. The Vich implant is formed from autogenic bone taken from the iliac crest of a patient. The Brantigan implant is formed of an inert metal such as stainless steel, cobalt-chromium-molybdenum alloys and titanium.
One problem associated with known implants is the difficulty in adapting an implant to meet the size requirements of a particular intervertebral receiving bed. For example, because anatomically all patients are different, the specific size of implant required for a surgical procedure will not be known to any certainty until a surgeon has prepared the intervertebral space for implantation. Thus, a surgeon must keep a variety of different size implants available for use or have means to alter the dimensions of the implant at his disposal.
Another problem associated with known implants constricted from bone is that the anatomical limitations of donor bone limit the size of the implant which can be formed from bone. As a result, bone having satisfactory strength characteristics may not be available for use as an implant because of size limitations.
Finally, yet another problem associated with known implants is their inability to accurately maintain the natural lordoses of the spine. Because of the irregular shape of the vertebral endplates, wedge-shaped implants and cylindrical dowels are incapable of supporting adjacent vertebrae in their natural orientation without substantially altering the shape of the vertebral endplate(s).
Accordingly, a continuing need exists for an intervertebral implant whose size may be easily altered by a surgeon during a surgical procedure to meet the size requirements of a particular implant receiving bed and for an implant capable of maintaining the natural lordoses of the spine without substantially altering the shape of the vertebral endplates.